Strict log reading mode

[kjnilsson]

We already have a "strict" or "absolute" means of attaching to a log by using {abs, Offset} - this mode will error if the offset does not exist in the log. However this does not take into account the case where retention overtakes a log reader. In this case it will simply just resume reading at the next segment.

Consider extending the absolute|strict "mode" to error whenever it tries to open the next segment it expects to exist and it doesn't and it isn't at the end of the stream.